This invention relates to a metallic magnetic powder, and more specifically to a metallic magnetic powder for magnetic recording.
In recent years, with the progress of magnetic recording equipment, there has been demand for magnetic recording media capable of recording with higher density than heretofore. As an effort to meet this demand, metallic magnetic powders have been proposed and employed which excel the oxide type magnetic powders in both coercive force and saturation magnetic flux density. However, the acicular particles of the powders are so short, less than one micron in length, and chemically so active that they tend to be oxidized in air with a gradual decrease in the saturation magnetic flux density, thus posing the problem of inadequate shelf stability.
Attempts to improve their oxidation stability so as to settle the foregoing problem have been made, for example, by oxidizing the metallic magnetic particle surfaces and thereby forming an oxide film thereon or by coating the metallic magnetic particles with various substances. The attempts made so far have included, for instance, forming a magnetic film on the metallic magnetic particle surfaces (Japanese Patent Application Public Disclosure No. 114769/1978), forming a higher fatty acid film thereon (Japanese Patent Application Public Disclosure No. 97738/1974), or depositing an amino-modified silicone oil (Japanese Patent Application Public Disclosure No. 77270/1979) or boron trialkoxide on the particles (Japanese Patent Application Public Disclosure No. 9802/1982). Still, these methods have not sufficiently rendered the metallic magnetic powders stable to oxidation, causing the powders to undergo serious deterioration of their magnetic properties in high-temperature, high-humidity atmospheres. For these reasons further improvements in the oxidation stability of the powders are being called for.
The present invention is based upon the discovery, arrived at after extensive investigations on ways of improving the oxidation stability of metallic magnetic powders, that a marked improvement is achieved by treating the particle surfaces with an alkyl group-containing dicarboxylic acid for its deposition thereon.